Negative active material, method of manufacturing its material, and lead acid battery

ABSTRACT

A negative active material is characterized by being prepared by adding a lignin having a unit structure represented by the formula (I) as the main structure to a lead oxide. Since the lignin of the formula (I) is added, the negative active material can be prevented from shrinkage due to charge/discharge.                  
 
(wherein R 1  is H, OH, COOH, SO 3 H, SH, C 6 H 5 , COO − , SO 3   − , R 2 C 6 H 4 , (R 2 ) 2 C 6 H 3 , or (R 2 ) 3 C 6 H 2 ; and R 2  is at least one member selected from among OH, COOR, SO 3 H, and CH 2 SO 3 H.)

TECHNICAL FIELD

This invention relates to a negative active material, a method ofmanufacturing its material and a lead acid battery.

BACKGROUND OF THE INVENTION

A lead acid battery is being widely used for a power source for startingan automobile engine and a power source for supplying electric power tovarious electrical equipments. The lead acid battery includes such aproblem that a high-rate discharge performance of a negative electrodeis deteriorated earlier than that of a positive electrode whencharge/discharge operations are repeated, so that a battery life islimited due to the negative electrode. The cause is supposed to beattributable to a fact that a negative active material shrinks due tocharge/discharge to cause a decrease in a surface area of the negativeactive material. In order to dissolve the above problem, a negativeactive material becomes used which is prepared by adding a lignin havinga unit structure represented by the formula (III) to a lead oxide.

In this instance, the lignin is a component included in a wood, and is aby-product produced when manufacturing pulp in a paper making factory.Since there are many processes for manufacturing pulp, it can be saidthat there are so many kinds of the lignin corresponding to thoseprocesses. The lignin of the formula (III) is called lignosulfonatewhich is produced by a method of sulfite digesting. Since sulfurous acidis used in this method, sulfonic acid group is introduced intoα-position of the side chain in the structure. The lignin of the formula(III) has a merit of large water-solubility, but has a demerit that itcan not be modified easily.

On the other hand, a Pb—Sb alloy has conventionally been used for apositive electrode grid in the lead acid battery. However, a type of thelead acid battery using the Pb—Sb alloy includes such a problem thatantimony in the alloy causes a lowering of a hydrogen over-voltage ofthe negative electrode, so that its maintenance becomes troublesomebecause a periodic supplement of water becomes required due to anincrease of the electrolyte's decrease. For this reason, a hybrid typelead acid battery using the Pb—Sb alloy which has an antimony contenthalf as much as a conventional battery, has been put in use. However, acalcium type lead acid battery using a Pb—Ca alloy is getting a largeshare in the market of the lead acid battery.

SUMMARY OF THE INVENTION

In the negative active material produced by adding the lignin of theformula (III) to the lead oxide, there has been such a problem that aneffect by the lignin, i.e. an effect to dissolve an earlierdeterioration of the high-rate discharge performance of the negativeelectrode, is weakened due to a gradual deterioration of the lignin. Thelignin has been deteriorated remarkably because a temperaturesurrounding the battery arises up to about 70° C. in a summer season,particularly when the lead acid battery is put in a engine compartmentof automobile.

While, in the calcium type lead acid battery, there is such a problem asan early decrease in a capacity of the positive electrode, because ofproducing a passive state on a surface between the positive electrodegrid and the positive active material due to over-discharge standing andbecause of forming a PbSO₄ layer on a surface of the positive electrodegrid due to repeating deep discharges. The hybrid type lead acid batteryhas included such a problem that the electrolyte's decrease becomeslarge to accelerate a battery deterioration particularly under ahigh-temperature environment, as compared with that of the calcium typelead acid battery. As a technology to dissolve such problems, thepositive active material produced by adding antimony compound to thelead oxide is disclosed in the JP 7-147160 A. According to thistechnology, the cycle life performance of the positive electrode can beimproved by adding the antimony compound of proper quantity. However,since an object of the above-mentioned technology is to improve thecycle life performance of the positive electrode, this is not effectivefor the lead acid battery in which the cycle life performance of thenegative electrode is inferior to the cycle life performance of thepositive electrode.

A first object of this application is to provide a negative activematerial which can improve a cycle life performance of a negativeelectrode.

A second object of this application is to provide a method ofmanufacturing a negative active material which can improve a cycle lifeperformance of a negative electrode.

A third object of this application is to provide a lead acid batterywhich can improve a cycle life performance of the battery by improvingcycle life performances of both a positive electrode and a negativeelectrode.

In order to accomplish the first object, the first invention of thisapplication comprises a negative active material characterized by beingprepared by adding a lignin having a unit structure represented by theformula (I) as the main structure to a lead oxide.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)

According to the first invention, the negative active material can beprevented from shrinkage due to charge/discharge because the lignin ofthe formula (I) is added to it. Since the lignin of the formula (I) ishard to be deteriorated even under a high-temperature environment, theeffect to prevent the negative active material from shrinkage can bekept for a long period even under the high-temperature environment.Therefore, according to this invention, the worsening of a high-ratedischarge performance of the negative electrode can be controlled for along period even under the high-temperature environment. Consequently,the life performance of the negative electrode can be improved.

The lignin of the formula (I) is one in which a sulfonic acid group isintroduced through methyl into an aromatic nucleus, and calledsulfo-methylated lignin. This lignin can be obtained by introducing asulfomethyl group into the aromatic nucleus of a kraft lignin.Sulfo-methylation is easily done by a treatment at high temperatureusing sodium sulfite and formaldehyde. The kraft lignin has a smallmolecular weight and a characteristic of being easily modified. Thesulfo-methylation is only an example of modification. The kraft ligninis obtained by a kraft digesting. In the kraft digesting, sodiumhydroxide and sodium sulfide are used and the sulfonic acid group is notintroduced into the structure of the lignin. The kraft lignin is hard tobe dissolved in water. However, the sulfo-methylated lignin has acharacteristic of being easily dissolved in water.

The lignin of the formula (I) is most generally used as sodium salt, butmay be used as potassium salt or other salts.

The reason why the lignin of the formula (I) is assigned as the mainstructure is that such a structure, in which one CH₂SO₃ ⁻ exists inplural such fundamental structures connected each other, may be thoughtof.

In order to accomplish the first object, the second invention of thisapplication comprises a negative active material characterized by beingprepared by adding a lignin having a unit structure represented by theformula (II) as the main structure to a lead oxide.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)

According to the second invention, the life performance of the negativeelectrode can be improved by virtue of its containing the lignin of theformula (II), in the same reason as the first invention.

The lignin of the formula (II) is one in which the sulfonic acid groupis directly introduced into the aromatic nucleus. This lignin can beobtained by treating the kraft lignin using sodium hydroxide, sodiumsulfite and potassium ferricyanide.

The reason why the lignin of the formula (I) is assigned as the mainstructure is that such a structure, in which one SO₃ ⁻ exists in pluralsuch fundamental structures connected each other, may be thought of.

It is preferable that the first and second inventions contain thefollowing concept (A).

(A) An adding amount of the lignin ranges from 0.2 to 0.6 mass %relative to the lead oxide.

According to the concept (A), the life performance of the negativeelectrode can be improved effectively.

In order to accomplish the second object, the third invention of thisapplication comprises a method of manufacturing a negative activematerial characterized by being provided with a process in which atleast a lignin having a unit structure represented by the formula (I) asthe main structure is added to a lead oxide.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)

According to the third invention, the negative active material of thefirst invention can be obtained.

In order to accomplish the second object, the fourth invention of thisapplication comprises a method of manufacturing a negative activematerial characterized by being provided with a process in which atleast a lignin having a unit structure represented by the formula (II)as the main structure is added to a lead oxide.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃or (R₂)₃C₆H₂; and R₂ is at least one member selected from amongOH, COOH, SO₃H, and CH₂SO₃H.)

According to the fourth invention, the negative active material of thesecond invention can be obtained.

It is preferable that the third and fourth inventions contain thefollowing concept (B).

(B) An adding amount of the lignin ranges from 0.2 to 0.6 mass %relative to the lead oxide.

According to the concept (B), the negative active material improvedeffectively in its life performance can be obtained.

In order to accomplish the third object, the fifth invention of thisapplication comprises a lead acid battery having positive electrodes andnegative electrodes, in which a negative active material composing thenegative electrode is characterized by being prepared by adding a ligninhaving a unit structure represented by the formula (I) as the mainstructure to a lead oxide.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)

According to the fifth invention, the life performance of the negativeelectrode can be improved because the lignin of the formula (I) is addedto the negative active material. Therefore, according to this invention,the life performance of the battery can be prevented from being limitedby the negative electrode. For this reason, the life performance of thebattery can be improved by using the positive electrode having a longlife.

In order to accomplish the third object, the sixth invention of thisapplication comprises a lead acid battery having positive electrodes andnegative electrodes, in which a negative active material composing thenegative electrode is characterized by being prepared by adding a ligninhaving a unit structure represented by the formula (II) as the mainstructure to a lead oxide.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)

Even in the sixth invention, the life performance of the battery can beprevented from being limited by the negative electrode because thelignin of the formula (II) is added, in the same reason as the fifthinvention.

It is preferable that the following concepts (C) & (D) are used in thefifth and sixth inventions.

(C) The positive electrode grid composing the positive electrode iscomprised of a lead alloy which does not contain antimony.

According to the concept (C), electrolyte's decrease can be controlledfurther because the positive electrode grid is comprised of the leadalloy which does not contain the antimony. Therefore, troublesomemaintenances such as supplying water etc. can be reduced.

Further, in the concept (C), it is preferable that the following concept(a) is used.

(a) The positive active material composing the positive electrode isprepared by adding antimony compound to a lead oxide, the added antimonycompound is Sb₂O₃, Sb₂O₅, or a mixture of them, and an adding amount ofthe antimony compound ranges from 0.05 to 0.2 mass % relative to thelead oxide.

According to the concept (a), the formation of PbSO₄ layer on thesurface between the positive electrode grid and the positive activematerial is controlled, because the positive electrode grid is comprisedof the lead alloy which does not contain the antimony and the antimonycompound is added to the positive active material, so that the lifeperformance of the positive electrode can be improved. Consequently, thelife performance of the battery can be improved further by combiningwith the improvement of the life performance of the negative electrode.

(D) An adding amount of the lignin ranges from 0.2 to 0.6 mass %relative to the lead oxide.

According to the concept (D), effects of the third and fourth inventionscan be obtained effectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT EXAMPLE 1

A lead acid battery was produced as follows.

Production of Negative Electrode

Manufacture of Negative Active Material

A lead oxide, a lignin, barium sulfate and an active materialreinforcing agent were stirred and mixed to prepare a negative activematerial. An adding amount of the lignin was 0.2 mass % relative to thelead oxide, an adding amount of the barium sulfate was 1.2 mass %relative to the lead oxide, and an adding amount of the active materialreinforcing agent was 0.03 mass % relative to the lead oxide. The activematerial reinforcing agent is a short fiber comprising polypropyleneresin. The lignin is one having a unit structure represented by theformula (I) wherein R₁ is OH. The lignin of the formula (I) is used assodium salt. Further, the lignin of the formula (I) is prepared bysulfomethylating a kraft lignin.

Production of Negative Electrode

Dilute sulfuric acid and water were kneaded together in the negativeactive material to prepare an active material paste. Then, the activematerial paste was filled in an expanded grid made of Pb—Ca—Sn alloy,cured and dried. Thereby, unformed negative electrodes were produced.

Production of Positive Electrode

Dilute sulfuric acid and water were kneaded together in a lead oxide toprepare an active material paste. Then, the active material paste wasfilled in an expanded grid made of Pb—Sb alloy, cured and dried.Thereby, unformed positive electrodes were produced.

Production of Lead Acid Battery

The positive electrode, the negative electrode and a separator made ofpolyethylene between them, were stacked to prepare an assembled element.This assembled element was inserted in a container made ofpolypropylene. Electrolyte comprised mainly of dilute sulfuric acidhaving a specific gravity of 1.28 (20° C.) was poured into the containerso as to carry out case formation. Thus, a lead acid battery wasproduced.

EXAMPLES 2 to 4

Lead acid batteries were produced with the same procedures as those ofExample 1, except that the adding amount of the lignin was varied as 0.4mass %, 0.6 mass %, and 0.8 mass %. These batteries were named asExamples 2 to 4, in this order.

COMPARATIVE EXAMPLE 1

A lead acid battery was produced with the same procedures as those ofExample 1, except that a lignin having a unit structure represented bythe formula (III) was used and its adding amount was varied as 0.2 mass%. The lignin of the formula (III) was used as sodium salt. The reasonwhy the adding amount of 0.2 mass % was selected was that the effect dueto the lignin of the formula (III) was best result.

The lead acid batteries of Examples 1 to 4 and Comparative example 1 hada nominal specifications of 8 Ah (10 HR) and 12V.

Test 1

The lead acid batteries of Examples 1 to 4 and Comparative example 1were subjected to cycle life tests under the following test conditions.

Test Conditions

Charge/discharge operations were repeated under such conditions as anambient temperature of 75° C., a discharge current of 4.17A, a dischargetime of 4 min., a charge current of 2.47A and a charge time of 10 min.Then, capacity tests were done every 480 cycles.

Capacity Test

The discharge operation was done at an ambient temperature of −18 ° C.with a current of 80 A, and a discharge capacity to reach a batteryvoltage of 6.0V was measured.

Result

Discharge capacities at 2,400 cycles and 4,800 cycles are listed inTable 1. In these batteries, a discharge capacity of Comparative example1 is assumed as 100%.

TABLE 1 Negative Life performance active material 2400 cycle: 4500cycle: Lignin Adding Discharge Discharge (Chemical amount capacitycapacity Battery formula) (Mass %) (%) (%) Example 1 formula (I) 0.2 104108 Example 2 formula (I) 0.4 109 112 Example 3 formula (I) 0.6 105 107Example 4 formula (I) 0.8 104 102 Comparative formula (III) 0.2 100 100example 1

Consideration

The cycle life performances of the lead acid batteries of Example 1 to 4were superior to that of the lead acid battery of Comparative example 1.

The lead acid batteries of Example 1 to 4 and Comparative example 1 weredisassembled and examined after completion of 4,800 cycles, and thefollowing facts became clear.

(1) In the lead acid battery of Comparative example 1, shrinkage of thenegative active material proceeded.

(2) In the lead acid batteries of Example 1 to 4, deterioration of thenegative electrodes as in case of Comparative example 1 was scarcelyrecognized. It can be thought that this is owing to the effect of thelignin.

(3) In the lead acid battery of Example 4, the accumulation of the leadsulfate due to the lack of the charge for the negative electrodes wasrecognized.

As seen from Examples 1 to 4 and Comparative example 1, the lifeperformance of the lead acid battery can be improved when the negativeactive material is used, which is prepared by adding the lignin havingthe unit structure of the formula (I) to the lead oxide. It ispreferable that the adding amount of the lignin ranges from 0.2 to 0.6mass %.

EXAMPLE 5

A lead acid battery was produced with the same procedures as those ofExample 1, only except for the following points.

(i) A material of the positive electrode grid made of Pb—Ca—Sn alloy wasused.

(ii) A material having a unit structure represented by the formula (II)was used as the lignin in the negative active material. R₁ in theformula is OH. The lignin of the formula (II) was used as sodium salt.The adding amount was 0.2 mass % same as the case of Example 1.

EXAMPLES 6 & 7

Lead acid batteries were produced with the same procedures as those ofExample 5, except that the adding amount of the lignin was varied as 0.4mass % and 0.6 mass % respectively. These batteries were named asExample 6 & 7, in this order.

COMPARATIVE EXAMPLE 2

A lead acid battery was produced with the same procedures as those ofExample 5, except that a lignin having a unit structure represented bythe formula (III) was used and its adding amount was varied as 0.2 mass%.

The lead acid batteries of Examples 5 to 7 and Comparative example 2 hada nominal capacity of 27Ah and positive electrode dimensions of alongitudinal length; 115 mm, a lateral length: 103 mm, and a thickness:1.5 mm.

Test 2

The lead acid batteries of Examples 5 to 7 and Comparative example 2were subjected to the cycle life tests under the following testconditions.

Test Conditions

Charge/discharge operations were done under such conditions as anambient temperatures of 25° C. and 75° C., a discharge current of 25A, adischarge time of 4 min., a charge current of 25A, and a charge time of10 min. Thereafter, a judgement discharge was done with a current of 272A, so that the battery life was judged to be ended when a voltage after30 seconds becomes below 7.2V.

Results are listed in Table 2. A cycle life number of the lead acidbattery of Comparative example 2 at 75° C. is assumed as 100%.

TABLE 2 Negative Life performance active material 25° C.: 75° C.: LigninAdding Cycle life Cycle life (Chemical amount number number Batteryformula) (Mass %) (%) (%) Example 5 formula (II) 0.2 128 121 Example 6formula (II) 0.4 145 142 Example 7 formula (II) 0.6 132 128 Comparativeformula (III) 0.2 110 100 example 2

Consideration

The cycle life performances of the lead acid batteries of Examples 5 to7 were superior to those of the lead acid battery of Comparative example2 even at an ordinary temperature of 25° C. and a high temperature of75° C. Particularly, at the high temperature of 75° C., the lifeperformances of the lead acid batteries of Examples 5 to 7 were superiorto those of the lead acid battery of Comparative example 2 by about 21%to 42%.

The lead acid batteries of Examples 5 to 7 and Comparative example 2were disassembled and examined after completion of the cycle life testat 75° C., and the following facts became clear.

(1) In the lead acid battery of Comparative example 2, the negativeactive material shrunk and the accumulation of the lead sulfate, i.e. socalled as “sulfation”, proceeded to cause a limitation of the batterylife by the negative electrode.

(2) In the lead acid batteries of Examples 5 to 7, the battery life wasexpired by the deterioration of the positive electrodes and thedeterioration of negative electrodes as occurred in Comparative example2 was not recognized. It can be thought that this is owing to the effectof the lignin.

(3) In the lead acid batteries of Examples 5 to 7, the electrolyte'sdecrease of them was small as compared with the lead acid batteries ofExamples 1 to 4.

As seen from Examples 5 to 7 and Comparative example 2, the lifeperformance of the lead acid battery can be improved when the negativeactive material is used, which is prepared by adding the lignin havingthe unit structure represented by the formula (II) to the lead oxide.Particularly, the life performances at high temperature are excellent.It is preferable that the adding amount of the lignin ranges from 0.2 to0.6 mass %. Since the positive electrode grid was made of the lead alloywhich does not contain the antimony, the electrolyte's decrease can becontrolled.

EXAMPLE 8

A lead acid battery was produced with the same procedures as those ofExample 5, only except for the following points.

A lignin in which R₁ in the formula (II) is SH is used, and the addingamount was varied as 0.1 mass %.

EXAMLES 9 to 12

Lead acid batteries were produced with the same procedures as those ofExample 8, except that the adding amount of the lignin was varied as 0.2mass %, 0.4 mass %, 0.6 mass % and 0.8 mass %, respectively. Thesebatteries were named as Examples 9 to 12, in this order.

The lead acid batteries of Examples 8 to 12 had a nominal capacity of 27Ah, and positive electrode dimensions of a longitudinal length: 115 mm,a lateral length: 103 mm, and a thickness: 1.5 mm.

Test 3

The lead acid batteries of Examples 8 to 12 were subjected to the cyclelife tests same as that of the test 2.

Results are listed in Table 3. A cycle life number of the lead acidbattery of Comparative example 2 at 75° C. was assumed as 100%.

TABLE 3 Negative Life performance active material 25° C.: 75° C.: LigninAdding Cycle life Cycle life (Chemical amount number number Batteryformula) (Mass %) (%) (%) Example 8 formula (II) 0.1 109 110 Example 9formula (II) 0.2 143 152 Example 10 formula (II) 0.4 145 160 Example 11formula (II) 0.6 128 148 Example 12 formula (II) 0.8 118 125

Consideration

The cycle life performances of the lead acid batteries of Examples 8 to12 were superior to those of the lead acid battery of Comparativeexample 2 even at an ordinary temperature of 25° C. and a hightemperature of 75° C. Particularly, at the high temperature of 75° C.,the life performances of the lead acid batteries of Examples 8 to 12were superior to those of the lead acid battery of Comparative example 2by about 10% to 60%.

The lead acid batteries of Examples 8 to 12 were disassembled andexamined after completion of the cycle life test at 75° C., and thefollowing facts became clear.

(1) In the lead acid batteries of Examples 8 to 12, the battery life wasexpired by the deterioration of the positive electrodes and thedeterioration of the negative electrodes as occurred in Comparativeexample 2 was not recognized. It can be thought that this is owing tothe effect of the lignin.

(2) In the lead acid batteries of Examples 8 to 12, the electrolyte'sdecrease of them was small as compared with the lead acid batteries ofExamples 1 to 4.

As seen from Examples 8 to 12 and Comparative example 2, the lifeperformance of the lead acid battery can be improved when the negativeactive material is used, which is prepared by adding the lignin havingthe unit structure represented by the formula (II) to the lead oxide.Particularly, the life performances at high temperature are excellent.The life performance at high temperature can be improved further in thelead acid battery using the lignin in which R₁ in the formula (II) isSH, as compared with the lead acid battery using the lignin in which R₁is OH. Since the positive electrode grid was made of the lead alloywhich does not contain the antimony, the electrolyte's decrease can becontrolled.

In order to examine an optimum adding amount of an antimony compoundwhen adding the antimony compound to the positive active material, leadacid batteries of Comparative examples 3 to 9 were produced.

COMPARATIVE EXAMPLE 3

A lead acid battery was produced as follows.

Production of Negative Electrode

Dilute sulfuric acid and water were kneaded together in a lead oxide toprepare an active material paste. Then, the active material paste wasfilled in an expanded grid made of Pb—Ca—Sn alloy, cured and dried.Thereby, unformed negative electrodes were obtained.

Production of Positive Electrode

A lead oxide and Sb₂O₃ were stirred and mixed together to prepare anactive material. An adding amount of the Sb₂O₃ relative to the leadoxide was 0.05 mass %. Then, the active material, dilute sulfuric acidand water were kneaded together to prepare an active material paste.Thereafter, the active material paste was filled in an expanded gridmade of Pb—Ca—Sn alloy, cured and dried. Thereby, unformed positiveelectrodes were produced.

Production of Lead Acid Battery

A lead acid battery was produced in the same as Example 1.

COMPARATIVE EXAMPLES 4 to 8

Lead acid batteries were produced with the same procedures as those ofComparative example 3, except that the adding amount of the Sb₂O₃ wasvaried as 0.1 mass %, 0.2 mass %, 0.3 mass %, 0.4 mass %, and 0.5 mass%, respectively. These batteries were named as Comparative examples 4 to8, in this order.

COMPARATIVE EXAMPLE 9

A lead acid battery was produced with the same procedures as those ofComparative example 3, except that the Sb₂O₃ was not added. The leadacid batteries of Comparative examples 3 to 9 had a nominal capacity of27 Ah, and positive electrode dimensions of a longitudinal length: 115mm, a lateral length: 103 mm, and a thickness: 1.5 mm.

Test 4

The lead acid batteries of Comparative examples 3 to 9 were subjected tothe cycle life tests under the following test conditions.

Test Conditions

Charge/discharge operations were done under such conditions as anambient temperatures of 75° C., a discharge current of 25 A, a dischargetime of 4 min., a charge current of 25 A, and a charge time of 10 min.Then, discharge was done for more than 56 hours on every 480 cycles.Thereafter, a judgement discharge was done with a current of 272 A, sothat the battery life was judged to be ended when a voltage after 30seconds became below 7.2V.

Results are listed in Table 4. A cycle life number of the lead acidbattery of Comparative example 9 is assumed as 100%.

TABLE 4 Adding amount of Sb₂O₃ Cycle life number Battery (Mass %) (%)Comparative 0.05 103 example 3 Comparative 0.1 110 example 4 Comparative0.2 107 example 5 Comparative 0.3 79 example 6 Comparative 0.4 62example 7 Comparative 0.5 55 example 8 Comparative 0 100 example 9

Consideration

The lead acid batteries of Comparative examples 3 to 5 were superior tothe lead acid battery of Comparative example 9 in the cycle lifeperformances. It can be thought that this is owing to the effect of theantimony compound added to the positive active material. On the otherhand, the electrolyte's decrease became large in proportion to theadding amount of the antimony compound, and the electrolyte's decreaseof the lead acid batteries of Comparative examples 6 to 8 became twiceor more as large as that of the lead acid battery of Comparative example9. For this reason, the life performances of the lead acid batteries ofComparative examples 6 to 8 were bad.

Similar results were obtained when Sb₂O₅ was used in place of the Sb₂O₃.

The lead acid batteries of Comparative examples 3 to 5 were disassembledand examined after completion of the cycle life test, and the followingfacts became clear.

In the lead acid batteries of Comparative examples 3 to 5; the positiveelectrodes were deteriorated a little, the negative active materialshrunk, and the accumulation of lead sulfate, i.e. so called “sulfation”proceeded, thereby causing the limitation of the battery life by thenegative electrode.

As seen from Comparative examples 3 to 9, the life performance of thepositive electrode can be improved when the antimony compound is addedto the positive active material by 0.05 to 0.2 mass %. Particularly, themost suitable adding amount was 0.1 mass %.

EXAMPLE 13

A lead acid battery was produced as follows.

Production of Negative Electrode

A negative electrode was produced in the same procedures as those ofExample 1. The adding amount of the lignin was 0.2 mass %.

Production of Positive Electrode

A positive electrode was produced in the same procedures as those ofComparative example 3, except that the adding amount of the Sb₂O₃ wasvaried as 0.1 mass %.

Production of Lead Acid Battery

A lead acid battery was produced in the same procedures as those ofExample 1.

EXAMPLE 14 & 15

Lead acid batteries were produced in the same procedures as those ofExample 13, except that the adding amount of the lignin was varied as0.4 mass % and 0.6 mass %, respectively. These batteries were named asExamples 14 and 15, in this order.

COMPARATIVE EXAMPLE 10

A lead acid battery was produced in the same procedures as those ofExample 13, except that a negative electrode was produced in the sameprocedures as those of Comparative example 2 and a positive electrodewas produced in the same procedures as those of Example 13.

Test 5

The lead acid batteries of Examples 13 to 15 and Comparative example 10were subjected to the cycle life tests under the same conditions asthose of the test 4.

Results are listed in Table 5. A cycle life number of the lead acidbattery of Comparative example 9 was assumed as 100%.

TABLE 5 Negative active material Lignin Adding (Chemical amount Cyclelife number Battery formula) (Mass %) (%) Example 13 formula (I) 0.2 125Example 14 formula (I) 0.4 142 Example 15 formula (I) 0.6 130Comparative formula (III) 0.2 110 example 10

Consideration

The cycle life performances of the lead acid batteries of Examples 13 to15 were superior to those of the lead acid battery of Comparativeexample 10 by about 25% to 42%.

The lead acid batteries of Examples 13 to 15 and Comparative example 10were disassembled and examined after completion of the cycle life test,and the following facts became clear.

(1) In the lead acid battery of Comparative example 10, the negativeactive material shrunk and the accumulation of lead sulfate, i.e. socalled as “sulfation”, proceeded to cause the limitation of battery lifeby the negative electrode.

(2) In the lead acid batteries of Example 13 to 15, the deterioration ofthe negative electrodes as occurred in Comparative example 10 was notrecognized. It can be thought that this is owing to the effect of thelignin.

(3) In the lead acid batteries of Example 13 to 15, the electrolyte'sdecrease of them was small as compared with the lead acid batteries ofExamples 1 to 4.

As seen from the above-mentioned description, in the lead acid batteriesof Examples 13 to 15, the life performance of the positive electrode canbe improved because the antimony compound is added to the positiveactive material and the life performance of the negative electrode canbe improved too because the lignin of the formula (I) is added to thenegative active material. Consequently, the life performance of thebattery can be improved further. It is preferable that the adding amountof the lignin ranges from 0.2 to 0.6 mass %. In addition, since thepositive electrode grid made of the lead alloy which does not containthe antimony, the electrolyte's decrease can be controlled.

Comparing the lead acid batteries of Examples 13 to 15, the lead acidbattery of Example 14 is most excellent in its life performance. Forthis reason, in Examples 16 to 18, the adding amount of the antimonycompound in the positive electrode was varied using the same negativeelectrode as that of Example 14.

EXAMPLES 16 to 18

Lead acid batteries were produced in the same procedures as those ofExample 14, except that the adding amount of the Sb₂O₃ was varied as0.05 mass %, 0.2 mass %, and 0.3 mass %, respectively. Tease batterieswere named as Examples 16 to 18, in this order.

Test 6

The lead acid batteries of Examples 16 to 18 were subjected to the cyclelife tests under the same conditions as those of the test 4.

Results are listed in Table 6. A cycle life number of the lead acidbattery of Comparative example 9 is assumed as 100%.

TABLE 6 Adding Negative active material Cycle amount of Lignin Addinglife Sb₂O₃ (Chemical amount number Battery (Mass %) formula) (Mass %)(%) Example 16 0.05 formula (I) 0.4 133 Example 17 0.2 formula (I) 0.4138 Example 18 0.3 formula (I) 0.4 101

Consideration

The cycle life performances of the lead acid batteries of Examples 16 to18 were superior to those of the lead acid battery of Comparativeexample 9. Particularly, the life performances of the lead acidbatteries of Examples 16 and 17 were superior to those of the lead acidbattery of Comparative example 11 by about 25% to 42%. Therefore, asobvious from Examples 14, 16 and 17, the adding amount of the antimonycompound to the positive active material preferably ranges from 0.05 to0.2 mass %.

The lead acid batteries of Examples 16 to 18 were disassembled andexamined after completion of the cycle life test, and the followingfacts became clear.

(1) In the lead acid batteries of Example 16 to 18, the deterioration ofthe positive electrode were not recognized. It can be thought that thisis owing to the effect of the antimony compound. However, theaccumulation of lead sulfate in the negative active material, i.e.“sulfation”, proceeded in proportion to the adding amount of theantimony compound.

(2) In the lead acid batteries of Example 16 to 18, the electrolyte'sdecrease of them was small as compared with the lead acid batteries ofExamples 1 to 4.

As seen from the above-mentioned description, in the lead acid batteriesof Examples 16 to 18, the life performance of the positive electrode canbe improved because the antimony compound is added to the positiveactive material and the life performance of the negative electrode canbe improved too because the lignin of the formula (I) is added to thenegative active material. Consequently, the life performance of thebattery can be improved further. Particularly, the life performance canbe improved further more, when the adding amount of the antimonycompound ranges from 0.05 to 0.2 mass %. In addition, since the positiveelectrode grid made of the lead alloy which does not contain theantimony, the electrolyte's decrease can be controlled.

ANOTHER EXAMPLES

(1) The same results were obtained in the above-mentioned Examples, evenwhen the lignin of the formula (II) was used in place of the lignin ofthe formula (I), or even when the lignin of the formula (I) was used inplace of the lignin of the formula (II).

(2) R₁ in the formula (I) or R₁ in the formula (II) is not limited tothe above-mentioned OH or SH. They may be H, COOH, SO₃H, C₆H₅, COO⁻, SO₃⁻, R₂C₆H₄, (R₂)₂C₆H₃, or (R₂)₃C₆H₂. R₂ is at least one member selectedfrom among OH, COOH, SO₃H, and CH₂SO₃. The same results were obtained inthe above-mentioned Examples even in these cases.

INDUSTRIAL APPLICABILITY

The negative active materials and the lead acid batteries of thisapplication can be extremely improved in their life performances, sothat they can provide a considerable industrial applicability.

1. A negative active material, comprising: a lead oxide, and a ligninhaving a unit structure represented by the formula (I) as the mainstructure.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)
 2. A negative active material,comprising: a lead oxide, and a lignin having a unit structurerepresented by the formula (II) as the main structure.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)
 3. A negative active material as setforth in claim 1 or 2, in which an amount of the lignin ranges from 0.2to 0.6 mass % relative to the lead oxide.
 4. A method of manufacturing anegative active material, comprising the step of adding at least alignin having a unit structure represented by the formula (I) as themain structure to a lead oxide.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)
 5. A method of manufacturing anegative active material, comprising the step of adding at least alignin having a unit structure represented by the formula (II) as themain structure to a lead oxide.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)
 6. A method of manufacturing anegative active material as set forth in claim 4 or 5, in which anadding amount of the lignin ranges from 0.2 to 0.6 mass % relative tothe lead oxide.
 7. A lead acid battery having a positive electrode and anegative electrode, in which a negative active material composing thenegative electrode is comprised of a lead oxide and a lignin having aunit structure represented by the formula (I) as the main structure.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)
 8. A lead acid battery having apositive electrode and a negative electrode, in which a negative activematerial composing the negative electrode is comprised of a lead oxideand a lignin having a unit structure represented by the formula (II) asthe main structure.

(wherein R₁ is H, OH, COOH, SO₃H, SH, C₆H₅, COO⁻, SO₃ ⁻, R₂C₆H₄,(R₂)₂C₆H₃, or (R₂)₃C₆H₂; and R₂ is at least one member selected fromamong OH, COOH, SO₃H, and CH₂SO₃H.)
 9. A lead acid battery as set forthin claim 7 or 8, in which a positive electrode grid composing thepositive electrode made of a lead alloy which does not contain anantimony.
 10. A lead acid battery as set forth in claim 9, in which thepositive active material composing the positive electrode is comprisedof a lead oxide and an antimony compound, the antimony compound isSb₂SO₃, Sb₂SO₅ or a mixture of them, and its amount ranges from 0.05 to0.2 mass % relative to the lead oxide.
 11. A lead acid battery as setforth in claim 7 or 8, in which an amount of the lignin ranges from 0.2to 0.6 mass % relative to the lead oxide.